Electrostatic coating apparatus



Aug. 19, 1 47- D. s. GUSTIN ETAL ELECTROSTATIC COATING APPARATUS Filed NOV. 29, 1941 W/Vl/V/O MM ATTORNEY INVENTORS D. -51 GUST/IV.

\\\\ iiiiiii Patented Aug. 19, 1947 Daniel S. Gustin and Albert W. Walnio, Bloomfleld, N. J assignors to Westinghouse'Electric Corporation, East Pittsburgh,

tion of Pennsylvania Pa., a corpora- Application November 29, 1941, Serial No.:420,940 (01. 91-18) Claims.

The present invention relates to the coating of vitreous material and has particular reference to an apparatus for applying a fluorescent coating to the envelope of a fluorescent lamp.

At the present time the customary method of coating fluorescent lamps is to suspend the fluorescent powders in a highly volatile binder and flush the inside of the envelope with the solution thus formed. The coated envelope or container is then allowed to dry for a short period, after which it is heated to a temperature sufliciently high to carbonize and drive off the binder.

The difllculty with prior alt methods resides in the fact that the lamp envelope or container must be handled several times, and since they are heated to a comparatively high temperature to volatilize the binder, an extensive cooling period is required before sealing-in the electrodes and completing the finished lamp. In addition, and more significantly, the firing of the coated container to drive off the binder aflfects the color characteristic of the finished lamp. Actual tests 7 have shown that any given fluorescent material, when subjected to ultra-violet radiations, will become excited with a great deal more brilliance or intensity than after applied to a container by a binder, the latter of which is subsequently driven off by volatilization.

Perhaps the explanation for this may be that a molecular layer of the binder remains beneath the particles of the fluorescent material after firing which is not removed, or such layer obtains insufllcient oxygen during the firing step to completely carbonize and burn oil, thus leaving a minute charred surface beneath th fluorescent particles. Whatever the explanation, the fact remains that either the fluorescent materiaLis, not excited by the ultra-violet to as high an intensity or a minute charred surface absorbs someoi the visible light, preventing it from getting out ;of the envelope, thus materially decreasing the'efifi'ciency ofthe lamp.

It is accordingly an objectiof the .presentzinvention to provide an apparatus ion-applying a uniform coating of fluorescent material-.1tog-the container for a fluorescent lamp andwhereinno binder is required to. form a.tenacious;;.b0ndbetween the fluorescent material jand.tl1'e:.container.

Another object of the present invention1is;-.the

precipitating dry fluorescent powder on the wall of a container for.- a fluorescent lamp to form a uniform coating thereon.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing wherein:

Fig. 1 is an elevational view partly in section of an apparatus for the coating of a container for a fluorescent lamp in acordance with the present invention;

Fig. 2 is a cross-sectional view taken on the line ll-il of Fig. 1;

Fig. 3 is an enlarged sectional view of a part of the apparatus shown in Fig. 1.

Fig. 4 is a fragmentary view of a completed fluorescent lamp in accordance with the present invention, and

Fig. 5 is a fragmentary view on an enlarged scale of a section of the lamp envelope showing the applied fluorescent coating.

Referring now to the drawing in detail, the apparatus as shown in Fig. 1 comprises a base 5 which may be supported above the floor by legs 6. Disposednear one end of the base is a retort or reservoir 1 of.- vitreous material such as glass, metalorithe like, which for convenience will be herein-referred to as the smoke generator. The purpose of this smoke generator is, as the name implies,,to convert the fluorescent powder into smokes To:,accomplish this, the fluorescent powderza isiinserted into the reservoir I after having been: groundto a very fine mesh. Naturally. the particularfluorescent material will vary depending'gupontheucolor of the light desired when the materialisexcited'by ultra-violet radiation. For example; if-i'agblue lamp is desired, calcium tungstateactiyated with leadmay beeemployed; while forwhItelight, a mixturezofmagnesium tungstate activatedlwith thoriazandzinc beryllium silicate --activa ted-i with manganeseamayt be used. As will be, noted? the reservoir;,is@.-providedi with an outlet Sat the bottom thereof andLthrQugh which the powderBfis-zied at a-uniform rat'eby a worm feed l0 amxedgto a shaft llextending-gthrough the reservoir. ancr'j ournallediinastopper. bearing is at the top ofjthe reservolnli'.

In ordertorotategthezwormfeedilll 'andshaft H at :a relatively, slowzspeedithe; latter is. provided with .a pulley. it; connected: by a belt. l5; passing provision of an apparatus; for electrostatically over bracketisupportedidlenpuileysg i.6 ,to,apu1ley I I. This pulley i1 is carried by a shaft extending from a reduction gear box It and this gear train is driven by an electric motor is. The outlet 3 of the reservoir 1 communicates with an annular passage or mixing chamber 20 provided with a Jet 22 through which a, gaseous medium under pressure, such as air or the like, is admitted from a conduit 23 by control of a valve 24. A small conduit 25 also communicates with the chamber 20 and with approximately the center of the reservmr l with the result that the gaseous medium, in fowing under pressure through the mixing chamber 20, sucks the finely divided powder 8 along with it, whereby it is blown into the resetvoir I in the form of a comparatively dense s'noke 23, the heavy fluorescent particles gravitating to the bottom of the reservoir 1, to be again fed through the outlet 8 by the worm feed iii.

If desired, the gaseous medium may also bypass the mixing chamber 20 by means of a conduit 21, under control of a valve 28, with the outlet of this conduit 21 being provided with a Jet 23 communicating with the chamber 20, adjacent the connection of the conduit 25 therewith, and in opposition to the direction of flow through the other jet 22, although this arrangement is by no means necessary for efllcient operation or smoke generation. A smoke outlet in the form of an extension 30 is provided in the reservoir 1 which is supported by a bracket 32 extending upwardly from the base for the purpose of forcing the smoke under pressure into the container to be coated.

The container or envelope 33 for a fluorescent lamp which is to be coated with the fluorescent material is arranged to be supported upon a pair of rollers 34 and 35, shown more clearly in Fig. 2. These rollers are carried by shafts 35 journalled in the bracket 32 as well as in a similar bracket 31, and in order to maintain the rollers in a desired position against the action of contraction and expansion thereof coil springs 38 bear against one end of the rollers 34, 35 and the bracket 31.

For the p rpose of rotating the rollers 34 and 35, as well as the vitreous container 33 which frictionally engages the rollers, a second reduction gear train 33 driven by an electric motor 40 is supported by the base 5. By reference now more particularly to Fig. 2, it will be noted that the driven gear 42 of the gear train 39 meshes with a gear 43 afllxed to the shaft 35 carrying the roller 34. An idler gear 44 is pivotally secured to the bracket 32 which meshes with the gear 43 and also with a similar gear 45 carried by the shaft 35 supporting the other roller 35 so that the latter is rotated in the same direction as the roller 34. A gas burner 46 provided with a plurality of jets 41 is positioned longitudinally of the rollers 34, 35 and container 33, so that the latter may be heated during rotation by the gas flames passing upwardly between the rollers, as shown in Fig. 2, with such burner connected to a conduit 43 leading to a source of gaseous fuel supply. The temperature of the container may range from 175 C. to 350 C. without changing the characteristics of the finished coating and it has been found that good results are obtained at a temperature of about 200 C.

As shown, the smoke outlet 33 from the smoke generator aligns coaxially with the container 33 when in position upon the rollers 34 and 35 so that the fluorescent material smoke is passed into the container. In order to accommodate containers of varying length, small tubular pieces of vitreous material or the like 49 are shown positioned at each end of the container to thus not as temporary extensions of the latter, and a suitable gasket or the like 50 is positioned between the tubular extension 49 and the bracket 32 to prevent the escape of smoke, thereby causing it to pass through the tubular extension into the container 33.

The finely divided fluorescent powder thus suspended in the air in the form of smoke is then ionized and electrostatically precipitated onto the inner surface of the container. A high voltage direct current generator 52 which generates a current ranging from 30 to 50 microamperes at a voltage of from 5000 to 15,000 volts is carried by the base 5. This generator may be of any suitable type, but it has been found convenient to employ a power pack comprising a transformer together with suitable rectifier tubes which will give the desired D. C. output energy. and since the generator per se forms no part of the present invention, it is believed unnecessary that it be further herein described in detail. It should sufllce to say that one side of the generator is grounded as shown at 53 to the metallic parts of the apparatus, while the other side is connected to an insulated terminal 54 supported by an upwardly extending bracket 55 from the base,5.

This bracket 55 also serves as one insulated -bearing for an elongated electrode 53 provided with a sharp pointed end 51 and which is further supported by an additional insulated bearing 53 likewise supported by a bracket 59 extending upwardly from the base 5. Electrical connection is made from the insulated terminal 54 to the electrode 56 by means of a brush contact 60 so that only the electrode 55 is at one polarity, while all other metal parts of the apparatus are at opposite polarity due to the ground connection 53.

The electrode 56 is moved so that its sharpened end 51 passes longitudinally and coaxially of the container 33 by a mechanism comprising a rackbar 62 having an angular projection 63 to which one end of the electrode 56 is secured. This angular projection is supported by small rollers or casters 54 engaging a track 55 secured to the base 5, and the rack-bar 52 meshes with a small gear 66 afllxed to a shaft 51 journalled to an upstanding bracket 58. A large pulley 59, also connected to the shaft 51, is rotated by a reversible electric motor 10 and belt connection I2. Suitable limit switches 13 are provided which are adapted to be engaged by adjustable projections 14 carried by the angular rack-bar projection 53 so as to stop the electrical motor 10 when the sharpened end 51 of the electrode 55 has reached its limit of travel.

In practicing the method of the present invention the apparatus above described is operated in the following manner. The container 33 to be coated is first placed upon the rollers 34 and 35 in direct communication with the outlet 30 of the smoke generator I, either with or without the tubular extensions 43 as required, and motor 40 started by the operator closing a control switch 15, thus casing rotation of the rollers 34 and 35 as well as the container 33 in the direction indicated by the arrows in Fig. 2. The gas jets 41 are then lighted to heat the container and the operator closes a reversing switch 15 to start the motor 10 so as to cause movement of the rackbar 62 and electrode 56 to the right as shown in Fig. 1. This accordingly causes the electrode 56 to slide through the insulated supported bearings carried by the brackets 55 and 59 until the sharpened electrode end 51 reaches the farthest end of. the container 33.- as shown in Fig. 1, at

which time the projection ll will engage the limit switch 13 to. stop the electric motor I0.

The electric motor. I9 is then started by closure of a switch 18 which thus rotates the worm feed Ill, forcing the finely divided fluorescent powder within the reservoir I through the outlet 9. The valve 24 is then opened, allowing the air or gas under pressure to pass through the chamber 20 where it sucks up the fluorescent powder, thus suspending it in the air in the form of smoke which is exhausted through conduit 25 into the reservoir 1. This smoke then passes out of the reservoir I through the outlet 30, and since the latter is in direct communication with the vitreous container 33 either with or without the tubular extensions 49, the smoke passes into the container with leakage thereof being prevented by the gasket 50.

The operator next closes a switch 'Il to connect the high voltage D. C. generator 52 to a source of electrical energy of the customary domestic potential of about 115 volts, which accordingly impresses a high D. C. voltage between the electrodes 56 and all metal parts of the apparatus. Also, since the gas flames are ionized, they form suitable electrodes for contacting the vitreous container 33 which, being hot, is rendered semi-conducting, not only by the gas flames, but by virtue of its contact with the metal rollers 34 and 35, thus impressing the high voltage across the vitreous container and the axially disposed electrode 56.

The motor III is again started by closure of the reversing switch 16 so as to withdraw the electrode 56 from within the container 33. As the sharpened end 51 is moved relatively slowly, the high voltage impressed between the electrode 56 and the vitreous container 33 ionizes the fluorescent powder 26 suspended in the air, thus causing a discharge, and the resulting high electrostatic field at the sharpened electrode end 51 precipitates the minute fluorescent particles onto the inner surface of the heated container, forming an exceptionally uniform layer. Precipitation of the fluorescent material follows the sharpened electrode end 51 as. it moves along the axis of the container 33 until the electrode end is completely withdrawn from the container, at which time the projection I4 carried by the angular portion 53 of the rack-bar 52 will engage the other limit switch 13 to again stop the electric motor 10.

In describing the operation of the apparatus in the manner above noted, it should be understood that the coating can be just as readily applied by the high electrostatic field generated and during movement of the electrode 56 into the container 33 in the same manner as described relative to movement of the electrode 56 out of the container. However, it is preferable to coat the container only during outward movement of the electrode 56 since obviously the electrode must be outside of the container in order to remove the latter from the rollers. In order to save time so as to coat envelopes during either direction of movement of the electrode 56, the smoke generator can be made so that it detachably connects to the container and pivots about an axis so as to allow withdrawal of the container from the electrode if desired.

Upon complete coating of the container or envelope 33, it is removed from the apparatus ready for fabrication into a finished fluorescent lamp 80, as shown in Fig. 4. The filamentary 6 electrodes 82 and 83 are sealed into the ends of the envelope in the manner well known in the art, and after evacuation the lamp is filled with a gaseous medium. such as argon, neon, or a mixture thereof, together with a small quantity of mercury. By reference more particularly to Fig.5,

it will be seen that the fluorescent particles are in direct adhesion with the interior envelope wall and there is an entire absence of any intervening onto the glass bulb or container for a fluorescent lamp. Moreover, since the coating is applied while the bulb is hot, it is possible to combine the coating operation with glass tube making machines in such manner that the glass never becomes cold from the time it is drawn until after it is completely coated. Inasmuch as no binder is required, a closer tenacious uniform coating results which is substantially one layer thick and the inherent fluorescent properties of the material are in no way impaired, thus not only increasing the efficiency of the light output from the completed fluorescent lamp, but also producing an entirely different color of the light from that of a lamp in which a binder is used. A further economy resulting from the operation of the present invention resides in the fact that substantially all of the fluorescent material is used and none is lost.

Although one specific embodiment of the present invention has been shown and described, it is to be understood that still further modifications thereof may be made without departing from the v age electrostatic field during its passage through I said container to cause ionization of the suspended fluorescent particles and precipitation thereof onto the surface of said container.

2. An apparatus for applying a coating to the vitreous container for a fluorescent lamp comprising a smoke generator operable to cause the suspension of finely divided fluorescent powder in a gaseous medium to form a smoke, means for connecting said smoke generator to said container to be coated to cause the smoke to pass therethrough, means for heating said vitreous container to render it electrically conducting, means for rotating said container simultaneously with the passage of smoke therethrough, and means including said heated vitreous container and operable to cause said smoke to be subjected to a high voltage electrostatic field during flow in said container to cause ionization of the suspended fluorescent particles and precipitation thereof onto the surface of said container.

3. An apparatus for applying a coating to the vitreous tubular container for a fluorescent lamp comprising a smoke generator operable to cause the suspension of finely divided fluorescent powder in a gaseous medium to form a smoke, a pair of rollers for supporting said container and for causing rotation thereof, a passageway interconnecting said smoke generator and said container to be coated for causing the passage of said smoke longitudinally of said container, a source of heat for heating said vitreous container to render it electrically conducting, an electrode disposed ad- Jacent the wall of said heated vitreous container, and a high voltage source of electrical energy connected to said electrode and to said heated vitreous container to cause a discharge with attendant ionization of the suspended fluorescent particles and precipitation thereof onto the surface of said container.

4. An apparatus for applying a coating to the vitreous tubular container for a fluorescent lamp comprising a smoke generator operable to cause the suspension of finely divided fluorescent powder in a gaseous medium to form a smoke, a pair of rollers for supporting said container to be coated and for causing rotation thereof, a passageway interconnecting said smoke generator and said container for causing the passage of said smoke longitudinally of said container, 9. source of heat for heating said vitreous container to render it electrically conducting, an elongated electrode disposed coaxially with the axis of said heated vitreous container and provided with a sharpened end for concentrating a high electrostatic field thereat, and a high voltage source of electrical energy connected to said electrode and to said heated vitreous container to cause a discharge with attendant ionization of the suspended fluorescent particles and precipitation thereof onto the surface of the container by the high voltage electrostatic field at the sharpened end of the electrode.

5. An apparatus for applylns a coating to the vitreous tubular container for a fluorescent lamp comprising a smoke generator operable to cause the suspension of finely divided fluorescent powder in a gaseous medium to form a smoke, a pair of rollers for supporting said container to be coated and for causing rotation thereof, a passageway interconnecting said smoke generator and said container for causing the passage; of said smoke longitudinally of said container, a source of heat for heating said vitreous container to render it electrically conducting, an elongated electrode disposed coaxially with the axis of said heated vitreous container and provided with a sharpened end for concentrating a high electrostatic field thereat, a high voltage source of electrical energy connected to said electrode and to said heated vitreous container to cause a discharge with attendant ionization of the. suspended fluorescent particles and precipitation thereof onto the surface of said container by the high voltage electrostatic field at the sharpened end of the electrode, and mechanism for moving said electrode longitudinally of said container during rotation and heating thereof to cause movement of the concentrated high voltage electrostatic field along the axis of said container with resultant precipitation of the fluorescent material over the entire inner surface of said tubular container.

6. An apparatus for applying a coating to the vitreous tubular container for a fluorescent lamp comprising a smoke generator operable to cause the suspension of finely divided fluorescent powder in a gaseous medium to form a smoke, a pair of rollers for supporting said container to be coated and for causing rotation thereof, a source of heat for heating said container over its entire length to a temperature above about C. to render said vitreous container electrically conducting, a passageway interconnecting said smoke generator and said container for causing the passage of smoke longitudinally of said container during rotation and heating thereof, an elongated electrode disposed coaxially with the axis of said heated vitreous container and provided with a sharpened end for concentrating a high'electrostatic fleld thereat, a high voltage source of electrical energy connected to said electrode and to said heated vitreous container to cause a discharge with attendant ionization of the suspended fluorescent particles and precipitation thereof onto the surface of said container by the high voltage electrostatic field at the sharpened end of the electrode, and mechanism for moving said electrode longitudinally of said container during rotation and heating thereof to cause movement of the concentrated high voltage electrostatic field along the axis of said container with raultant precipitation of the fluorescent material over the entire inner surface of said tubular container.

7. An electrodeposition apparatus comprising the combination of means for supporting a container, a gas burner for heating a zone of the wall of said container, a source of unidirectional high potential having one side thereof connected to said gas burner which thereby serves as an electrode, a second electrode on the opposite side of the container wall from said gas burner and connected to the other side of said source of potential, and means for projecting a finely divided material into the field of said potential, whereby said material is caused to be deposited on the wall ofsaid container.

'8. Apparatus for applying a coating to a vitreous container comprising means for heating said vitreous container to make it electrically conducting, means for rojecting finely divided coating material into said container, and means including said vitreous container and operable to subject said coating material to a high voltage electrostatic field to cause said material to be electrically charged and deposited upon the surface of said container.

9. An electrodeposition apparatus comprising the combination of means for supporting a container, a gas burner for heating a zone of the wall of said container, a source of unidirectional high potential having one side thereof connected to said gas burner which thereby serves as an electrode, a second electrode on the opposite side of the container wall from said gas burner and connected to the other side of said source of potential, means for projecting a finely divided material into the field of said potential, whereby said material is-caused to be deposited on the wall of said container, and means for moving the field of said potential over the surface of said container by causing relative movement between an electrode and said container.

10. An electrodeposition apparatus comprising the combination of means for supporting a container, a gas burner for heating a zone of the wall of said container, a source of unidirectional high potential having one side thereof connected to said gas burner which thereby serves as an electrode, a second electrode on the opposite side of the container wall from said gas burner and 10 connected to the other side of said source of UNITED STATES PATENTS potential, a conduit connected to said container to enable a finely divided material to be pro- Number Name Date jected into the field of said potential, and appa- 2,094,242 Parker S pt. 1937 ratus for causing relative movement between 5 2,119,309 Batchelor M y 3 3 one electrode and said container to distribute the 2,216,252 Randall f 1940 field of said potential over the surface of said 2,123,327 Russel t a1 Aug. 30, 1933 container with attendant progressive deposition 1,693,345 Gustln 1929 of said material on the surface of said container. 2,247,963 Ransbulg y 1, 1941 FOREIGN PATENTS DANIEL S. GUSTIN. ALBERT w WAINIQ Number Country Date 254,175 Great Britain July 1, 1926 REFERENCES CITED OTHER REFERENCES The following references are of record in the 15 Journal f the Society of Glass Technology, file Of this Patent vol. XXVII, No. 119, Feb. 1943, pages as, 39. 

